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Barothermal treatment of the cast binary alloy Al–8 at % Si has been performed at 560°C/100 MPa/3 h. A microstructure with silicon particles with an average equivalent diameter of ~2.9 microns has been formed in the alloy. Barothermically treated silumin had a yield stress of 67.6 MPa, a tensile strength of 141.6 MPa, and a relative elongation of 34.1%. Cold deformation of the alloy to obtain a foil with a thickness of 16 microns has been realized. A decrease of the aluminum and silicon crystal lattice constants has been established, which is more noticeable at the maximum deformation of the alloy. When deformed, a textured alloy structure is formed with an axis of {100} along the rolling direction. The mechanical properties of the deformed alloy are determined, and the values of yield stress, tensile strength, and elongation equal to ~265 MPa, 305 MPa, and 5.5%, respectively, are obtained for a tape with a thickness of 900 microns. With a higher degree of deformation, for a tape with a thickness of 90 microns, these characteristics have values of ~146 MPa, 165 MPa and 1.4%, respectively, and for the foil with a thickness of 16 microns, ~180 MPa, 196 MPa and 0.3%, respectively.

A laser optoacoustic method for quantitative assessment of the volumetric porosity of cast dispersion-strengthened metal-matrix composite materials has been proposed and experimentally implemented. The method is based on a statistical analysis of the distribution of amplitudes of backscattered broadband pulses of longitudinal acoustic waves in the tested materials. Laser excitation and piezoelectric recording of ultrasound is implemented with one-way access to the test object using a special laser-ultrasonic transducer. Silumin-based composites reinforced with silicon carbide microparticles in various volume concentrations (0.033–0.135) and composites obtained by reaction injection moulding based on aluminum reinforced with intermetallic $${\text{A}}{{{\text{l}}}_{3}}{\text{Ti}}$$ (volume concentration 0.04–0.115) have been studied. For both types of composites, the distribution of amplitudes of backscattered ultrasonic signals is approximated by a Gaussian distribution function applicable for a large number of statistically independent quantities. The empirically obtained dependence of the half-width of this distribution on the volumetric porosity of composites of two different types is approximated by the same linear function regardless of the manufacturing technology, as well as of the type, size, and concentration of strengthening particles.

Technologies for the 3D printing of metallic powders are being increasingly extensively used around the world as alternatives to casting and machining to manufacture components of complex shapes and prototypes. Silicon-alloyed aluminum alloys are the most widely used materials in the selective laser melting technologies, which is caused by the price of these alloys and their high manufacturability for the layer-by-layer fused deposition, owing to their low susceptibility to hot cracking under thermal and shrinkage stresses. High rates of cooling the melt facilitate the formation in the material of ultradispersed silicon-containing phases, which results in increased strength. In the article, exemplified by two cast alloys (AK7ch and AK9ch), the speeds of the process of building up the products by the selective laser melting technology have been determined at a laser-beam power of 300 and 325 W and an energy density within the range 89–32 J/mm3. It is shown that, for the AK9ch alloy, lower porosity values are achieved within the investigated energy density range when compared with the AK7ch alloy and better mechanical properties of the alloy with a higher silicon content are achieved within the range of lower laser-beam energy densities than for the alloy with a lower silicon content. The mechanical properties of the materials produced under the optimal selective laser melting conditions comply with the most stringent requirements for the mechanical characteristics of the castings of the AK7ch alloy upon heat treatment.

The microstructure, the phase composition, the component distribution, and the grain structure of the commercial eutectic Al–12.2 Si–0.2 Fe (at %) silumins formed at cooling rates of 102 and 105 K/s are studied. Three phases are detected in the alloy after solidification at both cooling rates: α-aluminum, silicon, and an iron-containing phase. The bulk samples have a heterogeneous dendritic structure with large dendrites of an aluminum-based solid solution, and a eutectic lamellar mixture of aluminum and silicon filling the interdendritic space. The melt-quenched foils are characterized by a homogeneous microstructure over the thickness; however, they have a layered structure. The rapidly solidified foils also have a homogeneous granular structure through the thickness and no pronounced texture. The mechanisms of solidification and microstructure formation are proposed for both the bulk samples and the melt-quenched foils.

Tribological tests of a hybrid composite (Al–12Si)–40Sn prepared by sintering mixtures of powders of silumin and pure tin were carried out using the pin-on-disk scheme. It has been established that an increase in the sliding velocity decreases the wear intensity of the composite upon dry friction, while an increase of the load leads to the opposite result. The data obtained indicate that the main contribution to the wear of the composite comes from the delamination of strongly deformed subsurface layers of the material. With an increase in the sliding velocity, the mechanism of the wear does not change, but, because of the heat-induced softening of the material, wear particles of the steel counterbody are pressed into it that “plate” the surface of the sample and reduce its wear intensity.

The analysis of the gradient structure-phase states and nanohardness of hypoeutectoid silumin at 120 μm depth after the processing by high intensive electron beams in the regime of top layer melting has been carried out. It has been shown that depending on the depth to the surface of irradiation the electron beam processing leads to the dissolution of the primary inclusions of silicon and intermetallides and the formation of structure of high-speed cellular crystallization of aluminium and the grains of plastic eutectic. A 1.5‒2 fold decrease in the concentration of the alloying elements has been detected. The hardness of irradiated silumin changes in a nonmonotonous way and reaches the maximum values exceeding the hardness of the initial state by 3.8‒4.2 times in the layer located at 30–50 μm depth. The interpretation of the observed changes in structure and hardness on irradiation has been given.

An Al–Si eutectic alloy was synthesized by the selective laser melting (SLM) method using a pilot wrought Al-Si powder (of Russian AKD-12 grade) as the starting material. On the basis of electron microscopy, the microstructure of the SLM alloy was certified with EDS mapping of elements (Al and Si). It has been established that the main structural component is an Al-based solid solution with a cellular-dendritic structure (with an average cell size of ~500 nm). The Si phase, which is a component of the eutectic, is located at the boundaries in the form of rounded crystals about ten nanometers in size. This paper presents the results of measuring the mechanical and nanomechanical properties, which show the competitiveness of the use of the pilot (experimental) powder.

The structure, phase composition and tribological properties of surface layers of hypoeutectic silumin after the complex processing including the electroexplosion alloying with the yttrium oxide powder in different regimes and the subsequent electron beam processing have been analyzed by the methods of modern physical material science. With respect to the initial silumin the ≈20-fold increase in the wear resistance and ≈1.5-fold decrease in the friction coefficient have been detected. The complex processing is accompanied by the formation of the multiphase submicro—nanocrystalline layer up to 80 μm in thickness enriched by yttrium and oxygen atoms responsible for the multiple increase in the wear resistance. At the complex processing according to the first regime of electroexplosion alloying (EEA) (Y2O3 powder mass—0.0589 g, discharge voltage—2.8 kV) with the subsequent electron beam irradiation, the major phase of the modified layer is the solid solution based on Al (≈71.2 mass %), the remaining phases are SiO2, YAlO3, YSi2. The 1.5-fold increase in the mass of Y2O3 powder at EEA and 1.1-fold decrease in the discharge voltage is accompanied by the increase in the quantity of phases, the significant (more than 2.5-fold) decrease in the content of the solid solution based on Al, the ≈2.2-fold increase in the content of silicon oxide, the presence of yttrium oxide and metallic yttrium.

—The hardness and the tribological properties of the AK10M2N silumin subjected to irradiation by a high-energy pulsed electron beam with an energy density of 35 J/cm2 are studied. As compared to the as-cast state, the microhardness of the surface layers increases by ≈20% (up to ≈1.2 GPa), the friction coefficient decreases by a factor of ≈1.3 (down to 0.42), and the wear parameter decreases by a factor of ≈6.6 (down to 0.74 × 10–3 mm3/(N m)). These changes are shown to be caused by the dissociation of silicon and intermetallic compounds in the surface layer during irradiation by a high-energy pulsed electron beam.

The structural phase states and silumin’s defect substructure of silumin hypoeutectoid composition subjected to electron beam processing with the following parameters: energy density—25 J/cm2, pulse duration—150 µs, number of pulses—3, pulsed repetition rate—0.3 Hz were analyzed by methods of modern physical material science. The irradiation of the surface leads to the melting of the surface layer, the structure formation of high-speed cellular crystallization of submicron dimentions and the repeated precipitation of the second phase particles. The cells formation of two types: those free from precipitations of the second phase and those containing the lamellar eutectic Al–Si was revealed. The cells are separated by the second phase interlayers containing the particles of Cu15Si14Al4Cu9, silicon and copper. As the distance from the surface of irradiation increases the layer containing the second phase inclusions of quasi—equilibrium shape are defined along with the crystallization cells. It is indicative of the occurance of the globularization processes of silumin’s structure on electron beam processing.

Compression tests of sintered (Al–12Si)–xSn composites have been carried out and it has been found that the flow curves of these composites consist of up to eight alternating linear and parabolic deformation stages. The strain-hardening coefficient θi of the material at each stage is constant. With increasing the order number of the stage i, θi decreases and can take a negative value. In the general case, θ = $$\theta _{i}^{n},$$ where n = 1 at the linear flow stage and n = 0.5 at the parabolic (odd) stage.

It is established that the electron-beam treatment of AK10M2N silumin by a pulsed electron beam with the specific energy of 35 J/cm2 leads to the increase in the surface layer microhardness from 0.99 up to 1.18 GPa with the simultaneous decrease in the friction coefficient by 1.3 times and in the wear coefficient by 6.6 times. After irradiation, a multilayer gradient structure is formed in the surface layer of the silumin. In the surface layer, there are no inclusions of the second phase, whereas in the deeper transient layer there are primary precipitations of intermetallic phase, which are the centers of aluminum crystallization. It is found that the changes in the mechanical and tribological properties of the silumin surface layers are associated with significant structural transformations, for instance, with the dissolution of silicon and intermetallics during irradiation of material with a high-intensity pulsed electron beam.

—Modern materials-science techniques are used to analyze the gradient structural-phase states and the nanohardness of hypereutectic silumin after high-current electron-beam melting of the surface layer. Electron-beam treatment is shown to dissolve silicon inclusions and intermetallic compounds observed in the initial state and form an aluminum cellular high-rate solidification structure and lamella eutectic grains. The content of alloying elements decreases by a factor of 1.5–2. The hardness of the irradiated silumin is found to change nonmonotonically and achieves its maximum at a distance of 30–50 μm from the surface. The maximum value is four times higher than the hardness of the unirradiated material. The radiation-induced changes in the silumin structure and hardness are explained.

The structure of cast AK10M2N silumin has been studied by scanning electron microscopy. The results demonstrate that the silumin is a multiphase material containing silicon and intermetallic inclusions. Irradiation of silumin with a high-intensity electron beam has been shown to be accompanied by melting of the surface layer, dissolution of the silicon and intermetallic inclusions, formation of a cellular crystallization structure, and secondary precipitation of submicron- and nanometer-sized second-phase particles. Dispersion of the structure of the surface layer is accompanied by an improvement of the mechanical properties of the silumin.

The effect of equal-channel angular pressing (ECAP) in an equal-channel stepped die on the microstructure and the mechanical properties of silumin AK9 (Al–Si–Mn–Mg) modified by a master alloy with nanostructured carbon in the form of fullerene black and synthesized glassy carbon particles formed during manufacturing the master alloy is studied. Silumins belong to nondeformable cast alloys; however, ECAP at 500°C makes its plastic deformation up to three passes possible. Three passes of deformation significantly refine the structure of the AK9 modified silumin. ECAP results in the refinement of silicon inclusions, which are of the fabrication origin and do not undergo plastic deformation.

Metallography, electron microscopy, and X-ray diffraction have been used to investigate structural transformations that take place in a 10-μm-thick surface layer in aluminum and Al–17% Si alloy under conditions of sliding friction and subsequent oxidation at 100 and 200°C for 1 h. Friction-induced deformation has been carried out at room temperature in air and at–196°C in liquid nitrogen by reciprocating sliding of a cylindrical indenter made of cubic boron nitride at a rate of 0.014 m/s and a load of 98 N. It is shown that deformation under these conditions forms nanocrystalline structures in the surface layer in aluminum and Al–17% Si alloy and increases their microhardness by a factor of 1.8–3.5. A high contact deformation and a high affinity of oxygen to aluminum and silicon cause the formation of anomalously supersaturated solid solutions of oxygen in aluminum and silicon in the surface layer of the alloy during friction. Oxidation at 100°C (1 h) of the deformed Al–17% Si alloy increases its microhardness due to the decomposition of anomalously supersaturated solid solutions of oxygen in aluminum and silicon and the formation of their oxides.

The influence of the volumetric porosity of isotropic metal-matrix composite materials, which are reinforced with ceramic microparticles, on the dispersion of the phase velocity of longitudinal acoustic waves is investigated. For this purpose, the method of broadband acoustic spectroscopy with a laser source of ultrasound and piezoelectric detection of nanosecond ultrasonic pulses is used. Composite samples based on a silumin matrix with added silicon carbide (SiC) microparticles in different mass concentrations (3.8–15.5%) were investigated. As the concentration of SiC particles in a sample increases, its porosity that is determined using the hydrostatic-weighing method also increases. The simultaneous increase in the filler concentration and porosity leads to the appearance of a dispersion of the phase velocity of longitudinal acoustic waves in the sample within the frequency range of 3–25 MHz. The obtained empirical relationship between the relative change in the phase velocity and the sample porosity can be used to obtain a proximate quantitative estimate of the bulk porosity of the isotropic metal-matrix composite materials.

The solidification of the AK12 alloy processed by a standard flux and a combined modifying flux, which significantly increases the mechanical properties of the alloy at a significant increase in the modifying effect time, is studied. The experimental results are simulated using the ProCAST software package.

The eutectic silumin modified by SiO2 nanoparticles is fabricated and studied. The sizes of particles and their concentration in the melt are varied. The strength of the silumin is found to complexly depend on the SiO2 nanopowder particle size. The noticeable increase in the hardness during heat treatment of the nanomodified silumin is mainly related to Guinier–Preston zones, and the contribution of grain refinement (precipitation hardening) is insignificant.

Phase transformations of an Al–20 at % Si high-silicon hypereutectic alloy have been studied by differential barothermal analysis at temperatures of up to 800°C in argon compressed to 100 MPa. High pressure has been shown to raise the melting point of the alloy by 5°C during heating and to lower the eutectic solidification temperature by 5°C during cooling in comparison with the canonical phase diagram of the Al–Si system. At a temperature of 553°C, heating and cooling lead to silicon dissolution and decomposition of the aluminum-based solid solution, respectively. After high-pressure solidification, the silicon particles in the alloy have a bimodal size distribution. Quantitative porosity characteristics in the alloy after a barothermal scanning cycle are similar to those in the as-prepared alloy. The lattice parameters of the silicon and aluminum remain unchanged. The microhardness of the aluminum matrix of the alloy corresponds to that of pure aluminum.

We describe barothermal processing (hot isostatic pressing) of an Al–10 at % Si binary alloy for 3 h at a temperature of 560°C and pressure of 100 MPa. The results demonstrate that this processing ensures a high degree of homogenization of the as-prepared alloy, which is chemically and structurally inhomogeneous. The morphology of the silicon microparticles in the material suggests that heat treatment of the Al–10 at % Si alloy at 560°C and a pressure of 100 MPa leads to a thermodynamically driven, essentially complete silicon dissolution in the aluminum matrix and the formation of a metastable, supersaturated solid solution, which subsequently decomposes during cooling. We analyze the associated porosity elimination process, which makes it possible to obtain a material with 100% relative density. Barothermal processing of the Al–10 at % Si alloy is shown to produce a bimodal size distribution of the silicon phase constituent: microparticles 1.6 µm in average size and nanoparticles 43 nm in average size. Barothermal processing is shown to reduce the thermal expansion coefficient of the alloy, and the microhardness of the two-phase alloy is determined. Based on the present results, we conclude that barothermal processing is an effective tool for eliminating microporosity from the Al–10 at % Si alloy, reaching a high degree of homogenization, and producing a near-optimal microstructure, which surpasses results of conventional heat treatment of the material at atmospheric and reduced pressures.

The structure, the phase composition, the surface morphology, the microhardness, and the tribological characteristics of the oxide layers of various thicknesses formed on AK9pch alloy during microarc oxidation are studied. A positive influence of a small addition (5 g/L) of nanosized silicon dioxide to an electrolyte on these characteristics of the oxide layers is revealed.

Centrifugal casting is used to form composite materials with a gradient structure. Hardening particles are shown to affect the hardness of the composite materials.

The laser optoacoustic method for porosity measurement of isotropic dispersion strengthened metal-matrix composite materials (CM) is proposed and experimentally realized. It is based on a laser thermooptical excitation of ultrasound, measurement of phase velocity of longitudinal acoustic waves in the studied material, and then application of a theoretical model for the dependence of phase velocity on porosity. The results of local porosity measurements (lateral resolution 1–2 mm) for the samples of CM based on AK12M2MgN silumin strengthened with silicon carbide particles with an average diameter 14 μm at different concentration are in agreement with the results of gravimetric measurements of the average sample porosity within the relative error of 10–15%.

A laser optoacoustic method for analyzing the effect of porosity on the local isotropic Young’s modulus of composite materials was proposed and experimentally implemented. Using as an example samples of a metal matrix composite based on silumin with reinforcing microparticles of silicon carbide, SiC, in various concentrations, it is shown that to provide an effective increase in Young’s modulus with increasing concentration of SiC, the porosity of the final sample should not exceed 2%.

This work was performed according to the plan of the Russian Academy of Sciences (theme no. 01.2.00613394, cipher "Impul's") and was supported in part by the Program of the Interdisciplinary Basic Research of the Ural Division of the Russian Academy of Sciences (project no. 09-M-23-2004) and by the Russia Foundation for Basic Research, project no. 09-03-12152 ofi_m. Optical and electron microscopy have been used to study microstructure of diffusion layers that are formed upon spreading of melts of the Al-12%Si and Al-20%Si alloys on steel St3.

The possibility of modification of the surface layers of cast plates of an antifriction AK9 aluminum alloy by electric-arc melting in a magnetic field is studied. The structure and mechanical and triboengineering properties of the AK9 alloy are studied in the initial as-cast state and after modification. It is shown that a fourpole magnetic system can control the sizes of the surface melting zone (width, depth) and the structural dispersity. The mechanical and triboengineering characteristics of the samples after processing are improved as compared to the initial material.

The phase equilibria in a hypoeutectic AK7 aluminum alloy (Al-7% Si-0.5% Mg silumin) are studied by differential barothermal analysis in the pressure range 5–131 MPa at temperatures up to 960 K. The baric dependences of the liquidus temperature during heating and the solidus and liquidus temperatures during cooling are found to have a minimum at 5 MPa. The solidus temperature during heating increases sharply as the pressure increases from 5 to 53 MPa and remains almost unchanged at a pressure p ≥ 53 MPa. The baric coefficients of the solidus and liquidus temperatures in the pressure range 5 ≤ p ≤ 53 MPa achieve ~0.6 K/MPa, which is much higher than the baric coefficient of the melting temperature of pure aluminum. A pT phase diagram is proposed for the AK7 alloy.

Processes of structure formation in iron-containing silumins remelted in a salt melt are analyzed. The effects of the chemical composition and temperature-time characteristics of the ionic medium on the phase composition of metallic materials are studied. The salt melt-silumin system is modeled in thermodynamic terms.